The present invention relates to an optical transmission repeater system, in particular, relates to a redundant light source system in that optical transmission repeater system, in which a plurality of repeaters are inserted in an optical transmission line for the digital signal transmission.
The reliability requested for an optical repeater utilized on land is not high, since the maintenance and repair of that repeater installed on land is possible, and a standby route can be easily installed. In addition to this, the reliability requested for an optical repeater on land can be satisfied by utilizing a conventional light source, like a semiconductor laser.
However, the reliability requested for repeaters installed in the sea-bottom is very high, since the maintenance and/or repair of those repeaters installed in the sea-bottom is rather difficult, and the standby route can not be installed for those submarine cable repeaters. Further, since the long distance submarine cable like the transPacific Ocean cable is installed under the deep sea-bottom. With the depth of the sea being up to 8,000 meters and the total length of such a submarine cable is over 8,000 kilometers the reliability requested for each of the repeaters is extremely high. The conventional submarine cable utilizing coaxial cable for the transmission of an electrical signal can satisfy the severe reliability requested for that system. However, in an optical transmission system which transmits an optical signal instead of an electrical signal, the reliability of a light source for generating the light is not so high as that of electrical components, and accordingly, the long distance submarine cable utilizing an optical transmission system has been impossible.